I built a circuit using a PCF8574 IÂ²c IO port extender to drive a transistor to switch relays. I used a current sinking scheme. So, output 1 = off, output 0 = on. The problem is, the relay always clicks on.
This is the schematic:
I measured the voltages and wrote them in (Irq should be Ir1). Vdd = 5V.
As you can see, there is 5.8V at the output of the PCF8574. I had expected there to be near 8V. If the output truly was high-impedance when 1, it would be, right?
I tested this circuit first by substituting an NPN transistor as an open-collector configuration and it worked fine.
What am I doing wrong here?